This invention relates generally to a method enabling improved separation of a sorbable gas constituent from a gas stream and, more particularly, to effecting such removal with a composite sorbent material providing increased sorption.
Various gas-adsorption processes have long been used to remove one or more constituents from a gas mixture. In doing so, the selection of a particular method is determined generally by the physical and chemical properties of the gas stream including concentration of the gas constituents, pressure, temperature, flow rate of the gas stream and still other factors. The desired separation is commonly effected by contacting a moving gas stream with a bed of solid adsorbent particles employing fixed or static bed operation, fluidized bed operation, moving bed operation or gas flow transfer contact wherein the powdered adsorbent particles have been dispersed in said gas stream. A known fluidized-bed type adsorption system is disclosed in U.S. Pat. No. 4,292,285 to remove compounds with an offensive odor like ammonia, benzene, diethylamine and still others from a gas mixture. A mixture of activated carbon and porous carbon impregnated with phosphoric acid or ammonium phosphate is used as the adsorbent material. It is reported that ammonia can be removed from a large amount of flowing gas even at a very low concentration. The gas stream to be treated is introduced into the adsorption chamber and odorous compounds are removed by adsorption therein. When the adsorbent material is saturated, the adsorption bed is regenerated with steam at 150.degree.-300.degree. C. The collected odorous gases are burned over a platinum catalyst. The regenerated adsorbent is thereupon transferred into the adsorption chamber for renewal of the adsorption-desorption cycle. In U.S. Pat. No. 4,283,204 there is disclosed a gas adsorption system to remove contaminants and impurities from a moving gas stream with a magnetically stabilized adsorption bed. Various adsorbent materials are said to be useful such as activated carbon and zeolites. Small adsorbent particles (50-1500 microns) are used to reduce the diffusional resistance during gas passage so adsorption equilibrium can quickly be reached. In order to prevent back-mixing of the solids and to reduce the pressure drop in the adsorbent bed, the adsorbent particles are mixed with a magnetizable component with an electromagnet being further employed to separate the micro fine particles in the effluent. For adsorbent regeneration, a portion of the purified gas stream is heated and used to flush the contaminants from the saturated adsorbent particles. A still further U.S. Pat. No. 4,689,062 reports separating ammonia from a synthesis plant purge gas at relatively high pressures around 1100 psig using zeolite adsorbent material in a three-bed adsorption system. Regeneration is reported to be carried out by purging the adsorption system with a hydrogen-rich gas stream at 400 psig in treating a two percent ammonia containing gas at 1200 psig.
As above indicated, the overall effectiveness of removing an undesired gas constituent from a gas mixture depends upon many factors. Factors that must be considered in carrying out an efficient and economical removal and/or recovery include capacity of the adsorbent material, selectivity of the adsorbent material with respect to all constituents in the gas stream, ease of desorbing the adsorbed constituent, desorption efficiency, and the costs involved. To further illustrate with respect to above cited adsorption processes wherein ammonia can be removed, any presence of moisture in the gas stream has now been found to reduce the adsorption capacity of certain adsorbents, such as zeolites. The affinity of zeolites and other polar-type adsorbent materials for moisture hinders the ammonia adsorption capacity so that nonpolar-type adsorbent materials such as activated carbon and activated alumina now prove more efficient. Since the attractive force between ammonia and polar-type adsorbent materials is also very strong, a relatively high desorption temperature in excess of 350.degree. C. also proves necessary to regenerate conventional adsorbent beds. Accordingly, it remains desirable to enhance the adsorptive separation of various gaseous substances from a gas stream in a novel manner.
It is therefore an object of the present invention to provide a more effective method for removing a sorbable gas from a gas mixture both with respect to the amount of particular gas constituent being sorbed as well as improving its subsequent recovery.
It is another object of the present invention to provide a sorption method having improved sorption capacity for various sorbable gas substances.
Still another object of the present invention is to provide a continuous sorption cycle for the removal of various gas constituents or contaminants and odorants from a process or waste gas stream enabling improved recovery of the removed gas constituent further accompanied by regeneration of the particular sorbent material being employed.
It is a still further object of the present invention to provide a continuous sorption cycle for the recovery of ammonia from a process or waste gas stream which is less sensitive to ambient conditions while providing a more efficient recovery.
These and other objects as well as advantages of the present invention will become more apparent from the following detailed description being provided upon preferred embodiments.